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Патент USA US2403527

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July 9, i946.
w. D. HERSHBERGER
2,403,527
PULSE-ECHO DISTANCE INDICATOR
Filed Jan. 5o, 194s
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2,403,527
Patented July 9, 1946
UNITED STATES PATENT OFFICE
2,403,527
PULSE-ECHO DISTANCE INDICATOR
William D. Hershberger, Princeton, N. J., assignor
to Radio Corporation of America, a corporation
o! Delaware
Application January so, 1943, serial No. 474,159
7 Claims. (ci. 25o-1)
2
l
My invention relates to pulse-echo systems for
The invention will be better understood from
indicating the presence of or the distance to
the following description taken in connection with
the accompanying drawing in which
reflecting objects.
The invention will be described as applied to
radio locator apparatus which transmits short
periodically recurring radio pulses and which re
ceives these pulses after they are reflected from
a reflecting object or surface. It is well known
that the distance to the reflecting object or sur
face can be determined by measuring the time
interval that has elapsed between the transmis
sion of a pulse and the reception of’ the reflected
Figure 1 is a block diagram of one embodi
ment of the invention; Figure 2 is a group of
graphs which are referred to in explaining the
invention; and Figure 3 is a circuit diagram of
a phase shifter that may be employed in the
apparatus of Fig. 1. In the several figures simi
lar parts are indicated by similar reference char
acters.
In Fig. 1 the invention is shown applied to a
pulse. This time interval is commonly measured
radio altimeter which comprises a sine wave os
cillator I0, a wave shaper I I for producing pe
by means of a cathode ray indicator tube.
riodic pulses 5, and a keyer I 2 for modulating
An object of the present invention is to pro
or keying a high frequency radio transmitter I3
vide in a pulse-echo system a method of and
by the pulses 5 whereby pulses of radio frequency
means for producing an indication when the dis
energy are radiated to the reflecting object or
tance to a reñecting object or surface falls out
side of predetermined distance limits.
surface. In the case of an altimeter mounted
A further object of the invention is to provide 20 on an aircraftto give an indication of an ob
an improved indicator for a radio altimeter of
stacle ahead as well as an indication of alti
the pulse-echo type.
tude, the radiation of the pulses is downward and
~
_
A still further object of the invention is to
provide an improved distance indicator for a
forward.
The reflected pulses are received and demodu
pulse-echo system.
25 lated by a receiver I6. The resulting pulses, in
dicated at I1, are supplied to an amplifier Ii!
In one preferred embodiment of the invention
which is connected to energize an indicator lamp
a radio altimeter is provided with two indicat
ing devices (two lamps, for example) which are
I9, and to an amplifier 2| which is connected
to energize an indicator lamp 22. The ampli
connected to receive the reflected pulses from
two amplifiers, respectively, under certain condi 30 fiers I8 and 2| are normally biased to cut-off
tions. These amplifiers are normally biased to
so that the received pulses I 1 will not energize
cut-ofi’ but are rendered operative periodically
the indicator lamps I9 and 22 unless the positive
at such intervals that the lamps are lighted only
pulses 23 and 24 are being impressed upon the
amplifiers I 8 and 2 I, respectively. Negative pulses
when the altitude is less than a predetermined
altitude limit or when the altitude or the distance 35 5' may be supplied to the receiver I6 over a
to a reflecting surface is greater than a predeter
conductor 20 to make it insensitive during the
mined altitude or distance limit and within the
transmission of a pulse.
Referring to Fig. 2, the positive rectangular
range of the altimeter. The latter condition isì
encountered either when the aircraft exceeds a
pulses '23 are initiated by the transmitter key
predetermined altitude or when there is an ob 40 ing pulses 5 and last for an adjustable period fol
stagëe such as a mountain in the path of the air
lowing the transmitted pulse. The positive rec
tangular pulses 24 are initiated at an adjustable
The above-mentioned periodic biasing or key
time after the termination of the pulses 23 and
ing of the amplifiers may be accomplished by
last until the occurrence of the next transmit
applying positive rectangular voltages thereto 45 ter keying pulse 5. It will be apparent that if
from trigger amplifiers or multivibrators. The
the reñected pulses arrive at the receiver at a
output from one trigger amplifier renders the
time between the end of a pulse 23 and the start
amplifier for one lamp operative for a short pe
of a pulse 24, neither of the indicator lamps I9
riod immediately following the transmission of a
and 22 will be lighted. If' lamp I9 lights, it in
50
pulse while the output from the other trigger am..
dicates that the aircraft is too low; if lamp 22
plißer renders the amplifier for the other lamp
lights, it indicates either that the aircraft is too
operative for a short period immediately preced
high or that there is an obstacle ahead.
ing the transmission oi’ a pulse. Between these
The rectangular pulses 23 and 24 may be ob
two periods the reception of a reflected pulse will
tained by supplying signal from the sine wave os
not light either one of the indicator lamps.
cillator I0 to the adjustable phase Shifters 3| and
cra
.
2,408, 527
32 (one of which is shown in detail in Fig. 3).
The sine wave signals from the phase shifters
3| and 32 are supplied to suitable wave shapers
33 and 34, respectively, to produce voltage pulses,
indicated at 38 and 31, which have a repetition
rate equal to the frequency of the sine wave sig
nals. Suitable wave shapers are well known and
may comprise, for example, a clipping tube or
tubes for changing the sine waves to waves that
are substantially rectangular, a diiferentiating
circuitl for obtaining narrow pulses from the sub
stantially rectangular waves, and additional clip
ping means.
cannot tell from this alone whether he has ex
~ ceeded the upper limit of altitude or is approach
ing an obstacle. This can be checked quickly. l
however, by adjusting the phase shifter 3l to see
what the altitude actually is, and, if necessary,
by also adjusting the phase shifter 32 to ilnd the
distance to the reflecting surface that has caused
the lamp 22 to light.
I claim as my invention:
l. A pulse-echo system comprising means i'or
transmitting pulses, means for receiving said
pulses after reilection from a surface nr object,
a pair of indicating devices, means for supplying
the received pulses to said indicating devices.
amplifiers or multlvibrators 38 and 38, respec
means for producing two- groups oi' control pulses
tively, at the proper .points so that pulse 36 termi
having a deilnite phase relation with respect to
nates the rectangular pulse 23 produced by trig
the transmitted pulses, and means responsive to
ger ampliiler 38, and so that pulse 31 initiates the
said two groups of control pulses for making said
rectangular pulse 24 produced by trigger ampliiler
indicating devices eiîective, respectively, to pro
38. The time relation between the several pulses 20 duce an indication only during a predetermined
is shown in Fig. 2. The start of the pulse 23 and
period following the transmission of a pulse and
' The pulses 36 and 31 are impressed upon trigger
the termination oi' the pulse 24 are determined
. by the keying pulse 5 which may be supplied
from the wave shaper Il over a conductor 4| to
an indication only during a predetermined period
‘ phase shift may be obtained by means of a re
ducing control pulses of positive polarity having
preceding the transmission of a pulse.
2. The invention according to claim 1 wherein
the trigger ampliñers 38 and 39. The time re 25 means is provided for adjusting the widths of
lations between the pulses 23 and 24 and the pulse
the control pulses in said two groups.
5 are shown in Fig. 2.
3. A pulse-echo system comprising means for
The phase Shifters 3| and 32 may be of the
transmitting periodically recurring pulses, means
type shown in Fig. 3 in which inductance coils/46
for receiving said pulses after reilection from a
and 4"l are placed so the axis of coil 48 makes an 30 surface or object, an indicating device, means in
angle of 90 degrees with the axis of coil 41 and
cluding an amplifier for supplying the received
have signals applied to them 90 degrees out of
pulses to said indicating device, said amplifier
phase to produce a. rotating iield. The 90 degree
normally being biased to cut-ofi', means for pro
sistor-capacitor network comprising resistors 5| 35 a deiinite phase relation with respect to the trans
and 52 and capacitor’53. A rotatably adjustable
mitted pulses. means for adjusting the duration
pickup coil 48 is mounted in the rotating field
of said control pulses, and means for applying
whereby the desired phase relation of input sig
said positive control pulses to said amplifier to
nal to output signal may be obtained by turning
make it eilective to pass the received pulses to
a phase adjustment knob 3i'.
said indicating device for the duration of each
It will be apparent that the time of occurrence
of the pulses 3B and 31 may be advanced or re
control pulse.
f
4. A pulse-echo system comprising means for
tarded by changing the adjustments of the phase
transmitting perodically recurring pulses, means
Shifters 3| and 32, respectively. Thus, as indi
for receiving said pulses after reñection from a
cated by the dotted line portions of the graphs 45 surface or object, an indicating device, means
in Fig. 2, the duration of the pulse 23 may be in
including an amplifier for supplying the received
creased or decreased to determine the lower al
titude limit at which the indicator lamp i9 will
light, and the starting time of the pulse 24 may be
changed to determine the upper altitude or dis
tance limit at which the indicator lamp 22 will
light. Therefore, as previously stated, one indi
cator will give a warning signal when the altitude
of the aircraft is below a predetermined adjusta
ble limit and the other indicator will give a warn
pulses to said indicating device, said ampliiler
normally being biased to cut-olf, means for pro
ducing control pulses having a known phase re
lation with respect to the transmitted pulses.
means for adjusting the phase of said control
pulses with respect to the transmitted pulses,
means for producing positive control pulses hav
ing a duration which is determined by the phas
ing oi’ said control pulses, and means for ap
ing when the altitude is above a predetermined
adjustable limit or when an obstacle is being
approached.
'I'he phase Shifters 3| and 32 preferably are cal
ibrated in distance so that the distance to the
plying said positive control pulses to said am
plitler to make it effective to pass the received
pulses to said indicating device for the duration
of each control pulse.
reñecting surface may be found by rotating the
transmitting pulses, means for receiving said
phase adjustment knobs 3 I ' or 32', respectively, to
the point where the indicator lamps I9 or 22, re
spectively, either light up if previously dark or
extinguish if previously lighted. For example,
the altitude may be determined by adjusting the
phase shifter 3| until the lamp i9 blinks on and
oil’ when the knob 3|’ is rotated left and right
very slight amounts. The pointer on knob 3|'
‘ 5. A pulse-echo system comprising means for
pulses after reflection from a surface or object,
a pair of indicating devices, means including a
pair of ampli?ers for supplying the received
pulses to said pair of indicating devices, respec
tively, said ampliñers normally being biased to
'cut-ofi’. means for producing two groups oi.' con
trol pulses of positive polarity having a known
phase relation and duration with respect to the
theln shows the altitude reading on the associated 70 transmitted pulses, means for adiusting the dura
sca e 6.
.
tion of said control pulses with respect to the
Similarly the altitude may be determined by
transmitted pulses, and means for applying said
adjusting the phase shifter 32 and reading the
two groups of positive control pulses to said am~
distance on' the scale 1. It may be noted that
pliners. respectively, to make them eiïective to
if, when in llight, the lamp 22 lights. the pilot
pass the received pulses to said indicating de
2,463,527
viäles for the duration ot each applied control
p se.
6. A pulse receiver for a system that includes
means for transmitting pulses. said receiver com
prising means for receiving said transmitted
pulses after they have been reilected from a
6
prising means for receiving said transmitted
pulses after they have been reñected from a
surface or object, two indicating devices; means
for supplying the received pulses to said indicat
ing devices, means for producing control pulses
that occur immediately following the transmis
surface or object, indicating means, means for
sion of a pulse, means for producing second con
sion of a pulse, means for producing second con
certain period between a iirst control pulse and
the following second control pulse, means re
trol pulses that occur immediately preceding the
supplying the received pulses to said indicating
transmission of a pulse but after the termina
means, means for producing iìrst control pulses
that occur immediately following the transmis 10 tion oi the iirst control pulses whereby there is a
trol pulses that occur immediately preceding the
transmission of a pulse but after the termina
sponsive to said iirst control pulses for causing
one of said indicating devices'to indicate when
tion oi the ilrst control pulses, and means respon
sive to said first and second control pulses for 15 the reflected pulses are received during the oc
currence of the iirst control pulses, and means
causing said indicating means to indicate whenl
responsive to said second control pulses for caus
the reil‘ected pulses are received during the oc
ing the other of said indicating devices to indicate
currence of either the first control pulses or the
when the reflected pulses are received during the
second control pulses.
'1. A pulse receiver for a system that includes 20 occurence of the second control pulses.
'
WILLIAM D. HERSHBERGER.
means ior transmitting pulses, said receiver com
Disclaimer
N. J. PULSE-Echo Drs'rsNcr:y
2,403,527.-Wül1'am D. Hershberger Princeton,
1946.
Disclaimer filed Nov. 5, 1949,
INDICATOR. Patent dated ‘ uly 9,
by the assignee, Radio Corporation 0j America.
Hereb enters this disclaimer to claims 3 and 4 of said patent.
[
°
Gazette DecemberI 27, 1949.]
,
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